Scanning probe microscopy probe and method for scanning probe contact printing

ABSTRACT

A method for fabricating scanning probe microscopy (SPM) probes is disclosed. The probes are fabricated by forming a structural layer on a substrate, wherein the substrate forms a cavity. A sacrificial layer is located between the substrate and the structural layer. Upon forming the structural layer, the sacrificial layer is selectively removed, and the probe is then released from the substrate. The substrate may then later be reused to form additional probes. Additionally, a contact printing method using a scanning probe microscopy probe is also disclosed.

FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0001] This invention was made with Government support under theNational Science Foundation under the NSEC Program (Grant No. 0118025)and by DARPA/AFOSR Grant No. ARMY NW 0650 300 F245. The government mayhave certain rights in this invention.

BACKGROUND

[0002] This invention relates generally to scanning probe microscopy(hereinafter “SPM”), and in particular, to an SPM probe formed with anintegrated tip and to a method of printing with an SPM probe.

[0003] A scanning probe microscope is an important instrument forscience and technology. One of the first scanning probe microscopes everdeveloped was called a Scanning Tunneling Microscope (STM). Anotherdevice within the scanning probe microscope family is an Atomic ForceMicroscope (hereinafter “AFM”). Nowadays, scanning probe microscopes areused to measure surface properties with atomic resolution. For example,scanning probe microscopes can be used to observe the structure ofdouble helix of DNA. The capability of scanning probe microscopes hasspread to include imaging of magnetic, optical, thermal, electrostaticcharges, and many more. Scanning probe microscopes are also used forbiological sensors as the static bending and resonant frequency of ascanning probe microscope is sensitive to the biochemical substancesabsorbed on it. Scanning probe microscopes are also used to performnanolithography, such as dip pen nanolithography, and nanomanipulation,that is, interacting with objects on a molecular and an atomic scale.

[0004] Scanning probe microscopes use a probe having a flexiblecantilever beam with a sharp tip attached at the distal end to performtheir measurements. The cantilever beam is very soft, often with a forceconstant on the order of 0.1 N/m or less. The tip is used to interactwith the surface of interest. In an AFM for example, the repulsive forcebetween the surface and the tip causes the cantilever beam to bend. Theminute amount of bending in the cantilever beam is picked up by usingsensitive instruments, such as by optical deflection. By raster scanningthe tip over a sample surface area, a local topological map can beproduced. If the tip of the probe is relatively sharp, the topologicalmap may be made with atomic resolution. Typically, the radius ofcurvature of tips range below 500 nanometers.

[0005] Needless to say, the SPM probe's cantilever beam with integratedtip is a performance limiting device in the overall scanning probemicroscope system. Many research groups as well as companies thatcommercialize the scanning probe microscope spend much time to developthe cantilever beam and the tip of the probe. Using current fabricationmethods, the cantilever beam is typically made of silicon nitride orsingle crystal silicon while the tip is typically etched by bulk siliconetching using wet etching chemicals or plasma etching. There are anumber of major drawbacks to existing fabrication methods. First, thetips are made sharp using a special, time-sensitive processes that isnot very efficient. Additionally, it is difficult to produce largearrays of tips with uniform sharpness. Moreover, the cantilevers aremade of inorganic thin films such as silicon nitride or single crystalsilicon which require a high temperature process and multiple processsteps, such as a bulk silicon etch, to produce. Furthermore, certainprocesses require removal of a substrate upon which the probes arefabricated upon in order to remove the probe, and more specifically, thecantilever, from the substrate. Thus, a need exists for an improvedmethod for fabricating an SPM probe.

[0006] Additionally, there is a need for an improved method forfabricating an SPM probe, including an array of SPM probes, using anefficient process, low cost materials, and a uniform profile. Suchprobes can then be used in a variety of ways, such as, for SPM,chemical/bio sensing, and nanolithography such as DPN.

[0007] There is also a need for an improved method for microcontactprinting. Microcontact printing (μCP) is a soft lithography methodcapable of creating micro-scale structures on a microscopic level.Microcontact printing uses a stamp to transfer chemical or biologicalmaterials, also known as “ink,” onto a solid substrate. Microcontactprinting creates impressions with the patterned stamp by placing thestamp near, or in contact with, the solid substrate. Microcontactprinting does not form images by dragging the stamp across the solidsubstrate. Repeated contact with the solid substrate can form dots,lines, curves, and other such shapes. The stamp can be made of a varietyof materials, such as metals, polymers, and elastomeric materials. Oneof the more commonly used elastomeric materials ispoly(dimethylsiloxane) (PDMS), which is an inert material that iscompatible with many chemical and biological inks. Microcontact printinghas been used to pattern self-assembled monolayers of alkanethiols,proteins, chemical precursors, and other biological materials on avariety of substrates. Microcontact printing has also been used totransfer chemical or biological materials (inks) onto a solid substrate.However, microcontact printing invariably requires a dedicatedphotolithography mask to produce inverse mold features, and is limitedwith respect to multi-ink and alignment registration capabilities.Additionally, the production of the mask can be relatively costly andtime consuming, particularly when sub-micrometer features are desired.Moreover, for many applications, such as the generation of proteomic andgene chips, well aligned, sub-micrometer scale features made of manydifferent inks are desirable. Thus, a need exists for a less costly andless time consuming method for microcontact printing.

BRIEF SUMMARY

[0008] According to one aspect of the present invention, a method forfabricating a scanning probe microscope probe is provided. The methodincludes forming a structural layer on a substrate. The substrate formsa cavity. A sacrificial layer is located between the substrate and thestructural layer. In one embodiment, the method further includesselectively removing the sacrificial layer. In one embodiment, themethod further includes releasing the structural layer from thesubstrate.

[0009] According to another aspect of the present invention, a methodfor fabricating a scanning probe microscope probe is provided. Themethod includes forming a structural layer on a substrate. Thestructural layer has a tip layer and a beam layer. The substrate forms acavity and the tip layer is in the cavity. The beam layer is on the tiplayer. A sacrificial layer is located between the substrate and the tiplayer. The method further includes patterning the structural layer.

[0010] According to another aspect of the present invention, a scanningprobe microscope probe is provided. The probe includes a tip having afirst material and a cantilever beam connected with the tip. Thecantilever beam includes a second material. The first material includesone of a metal, an oxide, and a polymer, and the second materialincludes one of a metal, an oxide, and a polymer.

[0011] According to another aspect of the present invention, a methodfor contact printing is provided. The method includes positioning ascanning probe microscopy probe having a tip near a substrate, whereinink is transferred from the tip to the substrate. The tip comprises apolymer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIGS. 1A-1D illustrate, in cross-section, process steps for thefabrication of an SPM probe, in accordance with one preferred embodimentof the invention.

[0013]FIGS. 2A-2E illustrate, in cross-section, process steps for thefabrication of an SPM probe, in accordance with one preferred embodimentof the invention.

[0014]FIGS. 2F-2G illustrate, in cross-section, process steps for thefabrication of an SPM probe, in accordance with one preferred embodimentof the invention.

[0015]FIG. 3A is a perspective view of a probe, in accordance with onepreferred embodiment of the invention.

[0016]FIG. 3B is a perspective view of a probe, in accordance with onepreferred embodiment of the invention.

[0017]FIG. 3C is a perspective view of a probe, in accordance with onepreferred embodiment of the invention.

[0018]FIG. 3D is a perspective view of a probe, in accordance with onepreferred embodiment of the invention.

[0019]FIG. 3E is a perspective view of a probe, in accordance with onepreferred embodiment of the invention.

[0020]FIGS. 4A-4D illustrate, in a side view, process steps for contactprinting with a scanning probe, in accordance with one preferredembodiment of the invention.

[0021]FIG. 5 is a top view of a pattern 68 formed using a scanning probecontact printing process, in accordance with one preferred embodiment ofthe invention.

[0022]FIG. 6 is a side view of an atomic force microscope (AFM) scanninghead connected with a probe, in accordance with one preferred embodimentof the invention.

[0023]FIGS. 7A-7C illustrate lateral force microscopy (LFM) images ofarrays of pixels generated using a scanning probe contact printingprocess, in accordance with one preferred embodiment of the invention.

[0024]FIG. 8 is a perspective view of a probe 27 having a flat top, inaccordance with one preferred embodiment of the invention.

[0025]FIG. 9 is a chart comparing the pixel diameter to the contact timebetween the tip and the substrate, in accordance with one preferredembodiment of the invention.

[0026]FIG. 10 illustrates a lateral force microscopy (LFM) image of twopatterns formed using a scanning probe contact printing process, inaccordance with one preferred embodiment of the invention.

[0027]FIGS. 11A-11D illustrate lateral force microscopy (LFM) images ofpatterns formed using a scanning probe contact printing process, inaccordance with one preferred embodiment of the invention.

[0028] It should be appreciated that for simplicity and clarity ofillustration, elements shown in the Figures have not necessarily beendrawn to scale. For example, the dimensions of some of the elements areexaggerated relative to each other for clarity. Further, whereconsidered appropriate, reference numerals have been repeated among theFigures to indicate corresponding elements.

DETAILED DESCRIPTION

[0029] The present invention describes a method for fabricating scanningprobe microscopy (SPM) probes. The probes are fabricated by forming astructural layer on a substrate, wherein the substrate forms a cavity. Asacrificial layer is located between the substrate and the structurallayer. Upon forming the structural layer, the sacrificial layer isselectively removed, and the probe is then released from the substrate.The substrate may then later be reused to form additional probes. Inthis manner, an SPM probe can be fabricated that has a well defined tip.Additionally, since the substrate can be reused, the materials cost forproducing the probe can be reduced. Moreover, the above-described methodfor fabricating a probe allows for a variety of materials to be used tomanufacture the probe.

[0030] Shown in FIGS. 3A-3D is a probe 27 suitable for use in a scanningprobe microscope. Please note that while FIGS. 1C-1D and FIG. 3,illustrate only one probe 27, and FIGS. 2B-2E illustrate two probes 27,29, an array of scanning probe microscopy (SPM) probes may have tens oreven hundreds of thousands of probes 27. In some instances, arrays ofSPM probes may have between one-hundred and ten million probes 27. Forthe sake of clarity, these additional probes have been left out of FIGS.1C-1D, FIGS. 2B-2E, and FIGS. 3A-3D.

[0031] Probe 27 includes a tip 30 comprising a first material and acantilever beam 28 comprising a second material. In one embodiment, thefirst material and the second material are the same material, while inanother embodiment, the first material and the second material aredifferent materials. Preferably, the first material and the secondmaterial each comprise a material selected from the group consisting ofmetals such as permalloy, copper, tungsten, titanium, aluminum, silver,and gold; oxides such as silicon dioxide, silicon oxide, and siliconoxynitride; nitrides such as silicon nitride and titanium nitride; andpolymers such as poly(dimethylsiloxane) (PDMS), polyimide, parylene, andelastomers such as silicone and rubber. The first and second materialsmay be formed by chemical reaction with the substrate 20, for example byoxidation, or by coating, for example with chemical vapor deposition oroblique angle physical vapor deposition.

[0032] The tip 30 is connected with the cantilever beam 28. The tip 30may take various forms and shapes, such as pyramidal, conical, wedge,and boxed. In one embodiment, the tip 30 takes a form having a base 40at one end and a point 42 at another end opposed to the base 40, such asa pyramid, a wedge, and a cone. The width of the tip 30 at the base 40is greater than the width of the tip 30 at the point 42, as illustratedin FIG. 3A and FIG. 2E. In one embodiment, the tip 30 takes the form ofa wedge, as illustrated in FIG. 2E, wherein the width of the tip 30 atthe base 40 is greater than the width of the tip 30 at the point 42, asillustrated in FIG. 2E. In one embodiment, the tip 30 takes the form ofa pyramid, as illustrated in FIG. 3A. Preferably, the tip 30 has aheight “H” of defined as the distance from the base 40 to the point 42,as illustrated in FIG. 3A. Preferably, the tip 30 has a radius ofcurvature “R” defined at the point 42, as illustrated in FIG. 3A.Preferably, the height “H” is between 1 and 100 microns and the radiusof curvature “R” is less than 350 nanometers, more preferably less than100 nanometers, and most preferably less than 50 nanometers at the point42. The pyramidal shape of tip 30 includes a plurality of surfaces thatform a plurality of edges 37 and 39, as illustrated in FIG. 3A. Thesurfaces 39 and 37 are formed at angles α and β, respectively, withrespect to a line normal to the connecting surface 44, as illustrated inFIG. 3A. Preferably, the angles α and β are between 10° and 75°. In oneembodiment, the tip 30 takes a form having a base 40 at one end and aflat top 54 at an opposing end, as illustrated in FIG. 3E. The flat top54 allows for the production of larger pixels 66 than the point 42, inorder to increase throughput in applications where lower resolution isacceptable. Preferably, the flat top 54 has less surface area than thebase 42.

[0033] In one embodiment, the tip 30 and the cantilever beam 28 areintegrally formed, as illustrated in FIG. 2E and FIG. 3B. In oneembodiment, the tip 30 is flat and is integrally formed at one end ofthe cantilever beam 28, as illustrated in FIG. 3B. In one embodiment,the tip 30 coats at least one surface of the cantilever 28, asillustrated in FIG. 3C. In another embodiment, the tip 30 coats one endof the cantilever 28, as illustrated in FIG. 3D. In one embodiment, thetip 30 includes a flat surface 90 upon which a pattern of ink 60 may beformed, as described below and as illustrated in FIGS. 3B, 3C, 3D, 3E.The flat surface 90 does not have to be exactly flat. The flat surface90 is able to accept a plurality of inks 60 and a plurality of patternsare able to be formed upon the flat surface 90. The flat surface 90comprises a material such as photoresist; SU-8; metals such aspermalloy, copper, tungsten, titanium, aluminum, silver, and gold;oxides such as silicon dioxide, silicon oxide, and silicon oxynitride;nitrides such as silicon nitride and titanium nitride; and polymers suchas poly(dimethylsiloxane) (PDMS), polyimide, parylene, and elastomerssuch as silicone and rubber. Preferably, the flat surface 90 comprises apolymer.

[0034] The cantilever beam 28 has a connecting surface 44 opposed to amounting surface 46. Preferably, the mounting surface 46 is connectedwith a handle 134, as illustrated in FIG. 2E. In one embodiment, themounting surface 46 is connected with an adhesion island 132, asillustrated in FIG. 2E. Preferably, the cantilever beam 28 has athickness “t”, defined as the distance between the connecting surface 44and the mounting surface 46, of between 1 and 10 microns, a length “1”of between 100 and 1,000 microns, and a width “w” of between 10 and 500microns. In one embodiment, the probe 27 comprises individual actuatorson the cantilever beam 28 for height adjustment of the probe 27.

[0035] Shown in FIGS. 1A-1D, in cross-section, are process steps for thefabrication of an SPM probe 27 in accordance with one preferredembodiment of the invention. As illustrated in FIG. 1A, a substrate 20is provided. Preferably, the substrate 20 comprises a single crystalsilicon substrate, however, the substrate 20 may comprise othermaterials. Preferably, the substrate 20 comprises a thickness of 50 to1000 microns, and more preferably, 300 to 500 microns. Preferably, thesubstrate 20 has a top surface 21 that has been previously processed andcleaned to remove debris and native oxides.

[0036] A cavity 22 is formed in the substrate 20, and more particularly,in the top surface 21 of the substrate 20. Preferably, the cavity 22 isformed by etching a shape into the substrate 20, however other means forforming the cavity 22 may be used. In one embodiment, the cavity 22 isformed using anisotropic etching. Preferably, the cavity 22 is formed byetching the substrate 20 wherein the cavity is bound by at least threesurfaces that meet at a point. The size and shape of the cavity 22 maybe controlled by adjusting the size of a mask opening used to form thecavity 22, and the and the amount of time the for the etching of thecavity 22. In one embodiment, the cavity 22 forms a sharp point at thebottom of the cavity 22, resulting in a tip 30 with a point 42. While inanother embodiment, the bottom of the cavity 22 is flat, resulting in atip 30 with a flat top 54, as illustrated in FIG. 3E. Preferably, thesubstrate 20 is first oxidized and patterned followed by anisotropic wetsilicon etching in ethylene diamine pyrocatechol (EDP) to form theinverted cavity 22. EDP may be obtained from Transene Company (Danvers,MA). If the etching time is sufficiently long, the resulting cavity 22is bound by four silicon surfaces and will end at a sharp point. Forshorter etching durations, a flat bottom of varying sizes may be formed.The cavity 22 serves as a mold to create the tip 30 of the probe 27, asdescribed below. By adjusting the size of the mask opening and the wetsilicon etching time, the shape of the bottom of the cavity 22 can becontrolled. If the cavity 22 ends in a sharp point, then a sharp tip 30having a point 42 forms, as illustrated in FIG. 3A. However, if thecavity 22 ends in a flat bottom, then a tip 30 with a flat top 54 forms,as illustrated in FIG. 3E. Tips 30 with a flat top 54 can be used toproduce larger pixels 66 to increase throughput in applications wherelower resolution is acceptable. The shape of the cavity 22 forms a threedimensional geometry that is opposite the desired shape of the tip 30.The cavity 22 serves as a mold for the tip 30 of the probe 27, asdescribed below. Preferably, the cross-sectional area of the cavity 22,taken along a line that is generally parallel with the top surface 21,is greater near the opening of the cavity 22 than at the bottom of thecavity 22, where the point 42 of the tip 30 is formed.

[0037] Upon forming the cavity 22, a sacrificial layer 24 is formed onthe substrate 20, as illustrated in FIG. 1B. The sacrificial layer 24may be formed by chemical reaction with the substrate 20, for example byoxidation, or by coating, for example with chemical vapor deposition oroblique angle physical vapor deposition. The sacrificial layer 24 isdifferent from the material contained in the substrate 20. Multiplematerials may also be used to form the sacrificial layer 24. In oneembodiment, the sacrificial layer 24 comprises at least one of manytypes of materials such as photoresist; SU-8; metals such as permalloy,copper, tungsten, titanium, aluminum, silver, and gold; oxides such assilicon dioxide, silicon oxide, and silicon oxynitride; nitrides such assilicon nitride and titanium nitride; and polymers such aspoly(dimethylsiloxane) (PDMS), polyimide, parylene, and elastomers suchas silicone and rubber. Preferably, the sacrificial layer comprisesaluminum, such as aluminum (99.999%) which may be obtained from AlfaAesar (Ward Hill, Mass.). The thickness of the sacrificial layer 24 mayvary, however, preferably, the thickness of the sacrificial layer 24 isbetween 1 and 100 microns, and more preferably between 10 and 50microns.

[0038] Upon forming the sacrificial layer 24, a structural layer 26 isformed on the sacrificial layer 24, as illustrated in FIG. 1C. Thestructural layer 26 may be formed by chemical reaction, for example byoxidation, or by coating, for example with chemical vapor deposition oroblique angle physical vapor deposition. In one embodiment, thestructural layer 26 is formed by depositing thin metal films,electroplating, or spin on polymer deposition. Preferably, thestructural layer 26 comprises a material that is different from thematerials contained in the sacrificial layer 24. Multiple materials mayalso be used to form the structural layer 26. In one embodiment, thestructural layer 26 comprises at least one of many types of materialssuch as photoresist; SU-8; metals such as permalloy, copper, tungsten,titanium, aluminum, silver, and gold; oxides such as silicon dioxide,silicon oxide, and silicon oxynitride; nitrides such as silicon nitrideand titanium nitride; and polymers such as poly(dimethylsiloxane)(PDMS), polyimide, parylene, and elastomers such as silicone and rubber.In one embodiment, the structural layer 26 comprises a polymer, and morepreferably, an elastomer. Preferably, the polymer is formed by mixing aseries of precursors in viscous liquid form, and then pouring the liquidover the substrate 20 and into the cavity 22. Excess polymer is thenremoved using a moving blade, a process of which is described in moredetail in “Precision Patterning of PDMS Thin Films: A New FabricationMethod and Its Applications,” by K. Ryu and C. Liu, Sixth InternationalSymposium on Micro Total Analysis System (mTAS), Nara, Japan, 3-7November 2002.

[0039] In one embodiment, the structural layer 26 comprises a 10:1 (v:v)mixture of PDMS—SYLGARD™ 184 Silicone Elastomer Base and SYLGARD™ 184Silicone Elastomer Curing Agent. SYLGARD™ 184 Silicone Elastomer Baseand SYLGARD™ 184 Silicone Elastomer Curing Agent may be obtained fromDow Coming Corporation (Midland, Mich.). In one embodiment, thestructural layer 26 comprises HD-4000 polyimide. HD-4000 polyimide maybe obtained from HD MicroSystems (Wilmington, Del.). The thickness ofthe structural layer 26 may vary, however, preferably, the thickness ofthe structural layer 26 is between 1 and 100 microns, and morepreferably between 10 and 50 microns. In one embodiment, the structurallayer 26 includes a tip layer 48 and a beam layer 50 on the tip layer48. Preferably, the tip layer 48 is formed in the cavity 22, and morepreferably, the tip layer 48 fills up the entire cavity 22. In oneembodiment, upon forming the tip layer 48, excess amount of the tiplayer 48 are removed using chemical-mechanical polishing, etching, or asharp blade. In one embodiment, excess amount of the tip layer 48 areremoved using a moving blade. In one embodiment, the tip layer 48comprises a 10:1 (v:v) mixture of PDMS—SYLGARD™ 184 Silicone ElastomerBase and SYLGARD™ 184 Silicone Elastomer Curing Agent. Preferably, uponforming the tip layer 48, tip layer 48 is then cured at a temperature of70° C. to 110° C. for a duration of 20 to 40 minutes. Upon forming thetip layer 48, the beam layer 50 is formed on the tip layer 48. In oneembodiment, the beam layer 50 comprises a thin layer of HD-4000polyimide that is spin coated, patterned, and cured to form thecantilever beam 28. Preferably, the tip layer 48 and the beam layer 50comprise different materials. For example, in one embodiment, the tiplayer 48 comprises a polymer while the beam layer 50 comprises a metal.In one embodiment, the tip layer 48 and the beam layer 50 comprisepolyamide. In one embodiment, the tip layer 48 comprises a metal whilethe beam layer 50 comprises a polymer, such as polyamide or parylene. Inone embodiment, the tip layer 48 comprises an elastomer and the beamlayer 50 comprises polyamide. The formation of the structural layer 26should not disrupt the substrate 20 or the sacrificial layer 24. Uponforming the structural layer 26, the structural layer 26 is patterned toform a probe 27 having a cantilever beam 28 and a tip 30, as describedabove.

[0040] Upon forming the probe 27, the sacrificial layer 24 is removed,as illustrated in FIG. 1D. Preferably, the sacrificial layer 24 isremoved using a process or material that does not harm the substrate 20or the structural layer 26. In one embodiment, the sacrificial layer 24is removed using aluminum etchant which may be obtained from TranseneCompany (Danvers, Mass.). Upon removing the sacrificial layer 24, theprobe 27 is released from the substrate 20. The substrate 20 may thenlater be reused to form additional probes 27 since the geometry of thecavity 22 is not significantly damaged. In one embodiment, upon formingthe probe 27, the tip 30 is further sharpened. Preferably, the probe 27can be formed, in accordance with the above-described method, at a lowtemperature of no greater than 120° C.

[0041] By forming the probe 27 using the above-described method, the tip30 of the probe is well defined by the inverted cavity 22 and thereforethe process of forming a sharp tip 30, or a tip 30 with a small radiusof curvature is possible by controlling the geometry of the invertedcavity 22 instead of controlling the geometry of the tip 30 itself.Additionally, since the substrate 20 can be reused, the materials costfor producing the probe 27 can be reduced. Moreover, the above-describedmethod for fabricating a probe 27 allows for a variety of materials tobe used to manufacture the probe 27 in additional to allowing the tip 30and the cantilever beam 28 to comprise different types of materials.Furthermore, since the above-described method for fabricating a probe 27involves only two layers, a sacrificial layer 24 and a structural layer26, the method is highly efficient in comparison with prior methods, andthus allows for probes 27 to be formed at lower cost.

[0042] Shown in FIGS. 2A-2E, in cross-section, are process steps for thefabrication of an SPM probes 127 in accordance with one preferredembodiment of the invention. Elements in FIGS. 2A-2E have referencenumerals increased by one hundred from those for elements in FIGS. 1A-1Dsince they refer to like elements. As illustrated in FIG. 2A, asubstrate 120 is provided wherein at least one cavity 122 is formed inthe substrate 120, and more particularly, in the top surface 121 of thesubstrate 120. The shape of the cavity 122 forms a three dimensionalgeometry that is opposite the desired shape of the tip 130.

[0043] Upon forming the cavity 122, a sacrificial layer 124 is formed onthe substrate 120, as illustrated in FIG. 2B. Upon forming thesacrificial layer 124, a structural layer 126 is formed on thesacrificial layer 124. The structural layer 126 is different from thematerial contained in the sacrificial layer 124. The structural layer126 is then patterned to form at least one probe 127 having a cantileverbeam 128 and a tip 130, as described above.

[0044] In one embodiment, upon patterning the structural layer 126, anadhesion island 132 is formed on the structural layer 126, asillustrated in FIG. 2C. The adhesion island 132 may be formed bydepositing an adhesion layer and then patterning the adhesion layer toform an adhesion island 132. The adhesion layer comprises at least oneof many types of materials such as photoresist; SU-8; metals such aspermalloy, copper, tungsten, titanium, aluminum, silver, and gold;oxides such as silicon dioxide, silicon oxide, and silicon oxynitride;nitrides such as silicon nitride and titanium nitride; and polymers suchas poly(dimethylsiloxane) (PDMS), polyimide, parylene, and elastomerssuch as silicone and rubber. Preferably, the adhesion layer has athickness, that is the same as the height of the adhesion island 132, ofbetween 1 and 50 micrometers. A handle 134, which preferably comprises atransfer substrate, is then formed on or placed on the adhesion island132. The handle 134 is thus connected with the adhesion island 132 andthe probe 127. Upon forming or placing the handle 134 on the adhesionisland 132, the handle 134 is then bonded to the adhesion island 132.Preferably, the adhesion island 132 is a soft polymer which can bepatterned to form an adhesion island. Preferably, upon heating theadhesion island 132, the adhesion island 132 is softened to help bondthe adhesion island 132 to the handle 134.

[0045] The handle 134 and the adhesion island 132 may be bonded in oneof many ways, such as spin on bonding using photoresist or an adhesivepolymer for adhesive bonding, which may be patterned (see for example“VOID-FREE FULL WAFER ADHESIVE BONDING” F. Niklaus, et al.); orhigh-temperature bonding, for example by heating the substrates togetherat about 1100° C. Preferably, the bonding process does not harm thesubstrate 20 or the probe 27. In one embodiment, the adhesion island 132is bonded to the handle 134 using low-temperature bonding at less than100° C. Alignment may be achieved using alignment mark, or usingfeatures present on the substrate 120, the handle 134, or the adhesionisland 132.

[0046] Upon forming the probe 127, which includes the handle 134, theadhesion island 132, and the structural layer 126 which forms the beam128 and the tip 130, the sacrificial layer 124 is removed, asillustrated in FIG. 2E. The substrate 120 may then later be reused toform additional probes 127.

[0047] In one embodiment, the structural layer 126 forms a hook 125, asillustrated in FIG. 2F. Upon forming the hook 125, the adhesion island132 is formed on the hook 125, as illustrated in FIG. 2G. The hook 125is used to improve the adhesion between the adhesion island 132 and thestructural layer 126, since the area between the adhesion island 132 andthe structural layer 126 may be small in a high-density probe array.

[0048] The individual processing steps used in accordance with thepresent invention are well known to those of ordinary skill in the art,and are also described in numerous publications and treatises,including: Encyclopedia of Chemical Technology, Volume 14 (Kirk-Othmer,1995, pp. 677-709); Semiconductor Device Fundamentals by Robert F.Pierret (Addison-Wesley, 1996); Silicon Processing for the VLSI Era byWolf (Lattice Press, 1986, 1990, 1995, vols 1-3, respectively); andMicrochip Fabrication: A Practical Guide to Semiconductor Processing byPeter Van Zant (4th Edition, McGraw-Hill, 2000). In order to etchthrough the substrate, techniques such as deep ion etching may be used(also known as the Bosch process).

[0049] The present invention also describes a method for contactprinting with an SPM probe, herein know as scanning probe contactprinting. The SPM probe is formed using any one of a variety oftechniques. Preferably, the SPM probe, is formed as described above.Upon forming the SPM probe, the SPM probe is then mounted onto ascanning probe microscope, such as an atomic force microscope (AFM), ora scanning tunneling microscope (STM). In one embodiment, the SPM probeis inked before being mounted onto the scanning probe microscope. Inanother embodiment, the SPM probe is inked upon being mounted onto thescanning probe microscope. Upon mounting the SPM probe onto the scanningprobe microscope, the SPM probe is then positioned and put near asubstrate, whereupon ink is transferred from the SPM probe to thesubstrate. The use of a scanning probe microscope to position the SPMprobe allows for a high degree of accuracy for aligning and positioningthe SPM probe to the substrate.

[0050]FIGS. 4A-4D illustrate, in a side view, process steps for scanningprobe contact printing using an SPM probe 227, in accordance with onepreferred embodiment of the invention. In one embodiment, the SPM probes227 are used in the scanning probe contact printing method to generatesub-micron patterns 68, as illustrated in FIGS. 4A-4D, and FIGS. 5-6.For example, if the tip of the probe 227 is coated with a fluid, such asan ink 60, then a surface 64 of a substrate 62, such as a substrate madeof glass, metal, silicon, or polymer, could be printed with the probes227 after they have received the fluid 60. Biological arrays maysimilarly be formed, for example by using fluids containing biologicalcompounds, such as nucleotides (RNA, DNA, or PNA), proteins (enzymes,antibodies, etc.), lipids, carbohydrates, etc. to spot a substrate, suchas glass, silicon, or polymers. The scanning probe contact printingmethod combines the advantages of contact printing and scanning probemicroscopy technologies by using a scanning probe 227 to transferchemical or biological materials onto the substrate 62.

[0051] The probe 227 can be any type of SPM probe. Preferably, the probe227 is a probe 27, as described above. Preferably, the scanning probemicroscopy (SPM) probe 227 used in this embodiment includes anintegrated tip 230 which comprises a material that adheres to fluid 60,such as, polymers, and more specifically, elastomers, likepoly(dimethylsiloxane), silicone, rubber, and polyimide. In oneembodiment, the tip of the probe 227 comprises a silicone elastomer.Preferably, the tip 230 comprises a polyimide, such aspoly(dimethylsiloxane), since polyimides are photodefinable andgenerally commercially available with a wide range of mechanicalproperties and achievable film thicknesses. The probe 227 includes acantilever beam 228. In order to effectively move the tip 230 around toprint arbitrary patterns 68, the probe 227, and more specifically, thecantilever beam 228 of the probe 227, has to have appropriate stiffness.The force constant (k) is used as a criterion in probe design. It iscalculated using the formula for a simple fixed-free cantilever beamunder small displacement assumption:${k = \frac{E\quad w\quad t^{3}}{4\quad l^{3}}},$

[0052] where E is the modulus of elasticity of the material, and w, t, lare the width, thickness, and length of the rectangular cantilever,respectively, as illustrated in FIG. 3. Preferably, the force constantfor the cantilever beam 228 is between 0.01 to 0.5 N/m, more preferablybetween 0.03 to 0.3 N/m, and most preferably between 0.04 to 0.2 N/m.

[0053] Upon forming the probe 227, the probe 227 is then mounted onto ascanning probe microscope instrument, such as an atomic force microscope(AFM) 70, as illustrated in FIG. 6. While an atomic force microscope isillustrated in FIG. 6, the probe 227 may be mounted onto any type ofscanning probe microscope, such as, but not limited to an AFM or an STM.

[0054] Upon forming the probe 227, ink 60 is attached to the tip 230 ofthe probe 227, as illustrated in FIG. 4B. Attacking ink 60 to the tip230 of the probe 227 is also referred to herein as inking the probe 227.The ink 60 may comprise any material which may be dispersed or dissolvedin a solvent, such as, nucleic acids, proteins, and peptides. In oneembodiment, the probe 227 is inked before being mounted onto thescanning probe microscope. In another embodiment, the probe 227 is inkedupon mounting the probe 227 onto the scanning probe microscope. Theprobe 227 may be inked in a variety of ways, such as a contact inkingmethod, as described below, and other such methods. For example, in oneembodiment, the probe 227, and more specifically, the tips 230 of theprobe 227, are inked by positioning the probe 227 near or in contactwith a second probe with an already inked tip. Preferably, the secondprobe is mounted onto a scanning probe microscope for accuratepositioning. In one embodiment, the probe 227 is inked by placing theprobe 227, and preferably, by placing the tip of the probe 227, near orin contact with a well filled with ink. In one embodiment, the probe 227is inked by placing the probe 227 near or in contact with a pad thatcomprises ink. Preferably, the pad comprises PDMS.

[0055] In one embodiment, the tip 230 of the probe 227 does not form apoint 42, but rather, the tip 230 forms a flat surface 290 which isinked, such as flat top 54 or 254, as illustrated by tips 30 in FIGS.3B, 3C, 3D, 3E, and 8. Preferably, ink 60 is patterned onto a flatsurface, such as flat surface 90 or flat surface 290, to form an inkpattern 92, an ink pattern 292, or a pattern of ink 60, as illustratedin FIGS. 3C and 8. The ink 60 may be patterned onto the flat surface 290by using a second probe 227 attached to a scanning probe microscope.Preferably, the ink pattern 92 comprises more than one pixel 66. In oneembodiment, the ink pattern 92 comprises a first and a second pixel 66,wherein the first pixel 66 does not come into contact with the secondpixel 66, as illustrated in FIG. 3C. Upon patterning the flat surface290 with ink 60, the flat surface 290 then is placed near, or comes intocontact with, the substrate 62. In one embodiment, upon patterning theflat surface 290 with ink 60, the flat surface 290 is placed near, orcomes into contact with, the substrate 62 a plurality of times in orderto make multiple copies of the patterned ink from the flat surface 290onto the substrate 62, or onto multiple substrates 62.

[0056] Upon mounting the probe 227 onto the scanning probe microscopeand attaching ink to the tip 230, also know as “inking the probe,” theprobe 227, the probe 227 is then positioned and placed near or broughtinto contact with a substrate 62, whereupon the ink 60 is transferredfrom the probe 227 to the substrate 62, as illustrated in FIGS. 4C and4D. The substrate 62 may be any type of material, such as silicon, gold,silver, aluminum, and paper. The tip 230 is positioned using thescanning probe microscope. Preferably, the tip 230 is placed near orbrought into contact with the substrate by moving the tip 230 towardsthe substrate 62 in a first direction D₁, as generally shown by thearrow in FIG. 4C. Once the tip 230 is placed near or brought intocontact with the substrate 62, ink 60 is transferred from the tip 230 tothe substrate 62. Upon transferring ink 60 from the tip 230 to thesubstrate 62, the tip 230 is moved away from the substrate 62 in asecond direction D₂, as illustrated in FIG. 4D, creating a dot or pixel66 as illustrated in FIG. 5. The size of the pixel 66 is dependant uponthe size of the tip 230 and the amount of time the tip 230 is in contactwith or near the substrate 62. Arbitrary, connected patterns 68, such aslines or blocks, can be formed by connecting multiple pixels 66, in amethod analogous to dot-matrix printing, as illustrated in FIG. 5. Theprobe 227 is compatible with commercial scanning probe machines. Theabove-described scanning probe contact printing method combines thechemical versatility and performance advantages of contact printing withthe production flexibility and accuracy of scanning probe microscopemachines. Additionally, no mask is necessary to produce arbitrarypatterns 68. Using the above-described scanning probe contact printingmethod, nanometer registration accuracy is feasible.

[0057] Without further elaboration it is believed that on skilled in theart can, using the preceding description, utilize the invention to itsfullest extent. The following example is merely illustrative of theinvention and is not meant to limit the scope in any way whatsoever.

EXAMPLE

[0058] The probe 227 was mounted and tested on a ThermomicroscopesAutoProbe® M5 atomic force microscope (AFM). An organic molecule,1-octadecanethiol (ODT), was used for the fluid 60. ODT (98%) may beobtained from Aldrich Chemical Company (Milwaukee, Wis.). The substrate62 was a silicon chip coated with a 5-nm-thick chrome layer for adhesionpromotion, and a 30-nm-thick gold layers. Preferably, the substrate 62is formed from a single crystal silicon wafers ({100} orientation),which may be obtained from International Wafer Service (Portola Valley,Calif.). Gold (99.99%) for the gold layers may be obtained from PureTech (Brewster, N.Y.). A chromium evaporation source (chrome platedtungsten rod) to form the chrome layer may be obtained from R. D. MathisCompany (Long Beach, Calif.). A contact inking method, as described in“Contact-Inking Stamps for Microcontact Printing of Alkanethiols onGold”, by L. Libioulle, A. Bietsch, H. Schmid, B. Michel, and EDelamarche, Langmuir, 1999, 15, pp. 300-304, was used to ink the tip 230of the probe 227 with ODT. The tip 230 comprises PDMS. A fluid pad, fromwhich the tip 230 was to received the fluid 60, was first prepared byimmersing a PDMS piece (4 mm*4 mm*0.3 mm) in 3 mM ethanolic ODT solutionfor at least 12 hours. After the fluid pad was impregnated with ODTsolution, the fluid pad was dried in a nitrogen stream for 10 seconds.The fluid pad was then stored in a small glass Petri dish before use.

[0059] The probe 227 was mounted on an AFM scanning head 70, asillustrated in FIG. 6. While the scanning head 70 could move in a zdirection, the sample stage of the scanning head 70 could move in x andy directions for rough alignment. For accurate movement in the printingprocess, the piezoelectric scanner 72 inside the scanning head 70 couldbe controlled by internal circuitry to expand or compress, moving theprobe in x, y, and z directions with nanometer scale accuracy.

[0060] In our experiments, inking was first done by bringing the tip 230into contact with a fluid pad, preferably, for between 5 and 15 minutes,and more preferably, for between 8 and 12 minutes. This allowed localtransfer of ODT from the fluid pad to the tip 230. The similarelasticity and surface characteristics of the fluid pad and the tip 230provided good contact at their interface, thus excessive contact forcewas not necessary. The quasi-continuous interface formed by both thePDMS surface of the fluid pad and the tip 230 also enabled homogeneoustransfer of fluid 60 from the fluid pad to the tip 230.

[0061] After the tip 230 was inked with a sufficient amount of fluid 60,in this case ODT, the tip 230 was moved to a designated location andlowered to contact the gold surface 64 of the substrate 62 to form apixel 66. After every formation of a pixel 66, the probe 227 was liftedand moved to another location to form another pixel 66. Because of thecapillary adhesive force at the interface between the tip 230 and thesubstrate 62, upon contact, the probe 227 could be lifted up a distanceof several microns without interrupting the contact and fluid transferbetween the tip 230 and the substrate 62. Hence contact printing couldbe conducted with even no or negative contact force between the tip 230and the substrate 62. In our experiments, all contact printings wereconducted with a contact force (F) between −200 nN to 200 nN. Pleasenote that the contact force readings of between −200 nN to 200 nN maynot be the actual contact force, however this is just representative ofthe contact force. As defined herein, the contact force (F) ortip-substrate interaction force is the z (vertical) component of theforce exerted on the probe tip 230 when the tip 230 is in contact withthe substrate 62. When the tip 230 is lowered to just contact with thesubstrate 62 without any overdrive, the contact force (F) is assumed tobe 0. Further lowering the probe handle (overdrive) will cause arepulsive force (+z direction) exerted on the tip 230 by the substrate62. If the probe handle 134 is withdrawn for a small distance, theadhesive force at interface between the tip 230 and the substrate 62will try to hold the tip 230 down on the substrate 62, thus exerting apulling (attractive) force (−z direction) on the tip 230. In both cases,the magnitude of the contact force (F) can be estimated as F=kΔz undersmall displacement assumption, where k is the force constant of thecantilever and Δz equals to the small displacement of probe handle 134.

[0062] The feature size of tip-based contact printing is affected byseveral factors, including the tip geometry, the tip-substrate, thecontact time, the relative humidity of environment, and other suchparameters. With other parameters set, the printed pattern size of thepixel 66 is proportional to the contact time of the tip 230. As anexample, FIGS. 7A-7C show lateral force microscopy (LFM) images of 3*3arrays of pixels 66 generated using the above described SP-μCP method.The printing probe tip 230 has a flat top 254 of 1.5 μm*1.5 μm, as shownin FIG. 8. The size of each image shown in FIGS. 7A-7C is 12 um*12 μm.The tip 230 of the probe 227 used to create the pixels 66 in FIGS. 7A-7Chas a flat top 254 of 1.5 μm*1.5 μm, as illustrated in FIG. 8. Bycomparison, we see that the feature size increases as the tip-substratecontact time is increased from FIG. 7A to FIG. 7C. For the image shownin FIG. 7A, the contact time between the substrate 62 and the tip 230was approximately 5 seconds and the diameter D of the pixel was 1.8 μm.For the image shown in FIG. 7B, the contact time between the substrate62 and the tip 230 was approximately 10 seconds and the diameter D ofthe pixel was 2.1 μm. For the image shown in FIG. 7C, the contact timebetween the substrate 62 and the tip 230 was approximately 20 secondsand the diameter D of the pixel was 2.4 μm. The environment temperatureused to create the pixels 66 shown in FIGS. 7A-7C was 21° C., and therelative humidity was 27%.

[0063]FIG. 9 shows the diameter of pixels 66 printed from ODT by a sharptip 230 with varying contact time between the substrate 62 and the tip230. A generally linear relationship between the diameter of a pixel 66and the contact time between the substrate 62 and the tip 230 can beobserved. The environment temperature used to create the pixels 66charted in FIG. 9 was 25° C., and the relative humidity was 55%. The tip230 of the probe 227 used to create the pixels 66 charted in FIG. 9 hasa radius of curvature R of 300 nm.

[0064] Lines and other complicated patterns 68 could be formed byplacing pixels 66 close to each other. FIG. 10 shows an LFM image of twopatterns 68, each forming lines with a length L of 10 μm. The size ofthe image shown in FIG. 10 is 30 um*30 μm. The width W of the linesformed in FIG. 10 is 890 nm. Each line comprises 20 pixels 66. Thecontact time between the substrate 62 and the tip 230 for forming eachpixel 66 in FIG. 10 was 60 seconds. The distance between each pixel 66in FIG. 10 is 500 nm. The environment temperature used to create thepixels 66 shown in FIG. 10 was 25° C., and the relative humidity was55%. The tip 230 of the probe 227 used to create the pixels 66 shown inFIG. 10 has a radius of curvature R of 300 nm.

[0065] Comparison results of lines generated with different contact timebetween the substrate 62 and the tip 230 are shown in FIGS. 11A-11D. Thesize of the image shown in FIGS. 11A-11D is 6 um*6 μm. Each linecomprises 20 pixels 66 with a distance between adjacent pixels 66 of 500nm. The environment temperature used to create the pixels 66 shown inFIGS. 11A-11D was 25° C., and the relative humidity was 55%. The tip 230of the probe 227 used to create the pixels 66 shown in FIGS. 11A-11D hasa radius of curvature R of 300 nm. In FIG. 11A, a pattern 68 in theshape of a line was formed with a contact time between the substrate 62and the tip 230 of 10 seconds because the size of each pixel 66 wassmaller than the distance between adjacent pixels 66. The width W of theline formed in FIG. 11A is 305 nm. In FIG. 11B the contact time betweenthe substrate 62 and the tip 230 to form each pixel 66 was 20 secondsand the width of the line formed is 434 nm. In FIG. 11C the contact timebetween the substrate 62 and the tip 230 to form each pixel 66 was 30seconds and the width of the line formed is 480 nm. In FIG. 11D thecontact time between the substrate 62 and the tip 230 to form each pixel66 was 60 seconds and the width of the line formed is 890 nm. Byadjusting contact time between the substrate 62 and the tip 230 and thedistance between adjacent pixels 66, a line having a width W of lessthan 500 nm or even less than 300 nm can be achieved. In one embodiment,the width W of the formed line is approximately equivalent to thediameter D of a pixel 66, as illustrated in FIG. 11A.

[0066] In the above-described scanning probe contact printing method,the amount of interaction force and lateral friction between the tip 230and the substrate 62 have also reduced the amount of wear to the tip230. The PDMS tip 230 used in the experiments showed no apparent changeof curvature radius after more than 24 hours of the scanning probecontact printing method. In addition, the scanning probe contactprinting method also proved an efficient method to fill the tip 230 withsufficient ink. Additionally, a cleanroom environment should improve thequality of the patterns 68 formed by the above-described scanning probecontact printing method.

[0067] Numerous additional variations in the presently preferredembodiments illustrated herein will be determined by one of ordinaryskill in the art, and remain within the scope of the appended claims andtheir equivalents. For example, while the examples provided above relateto silicon-based semiconductor substrates, it is contemplated thatalternative semiconductor materials can likewise be employed inaccordance with the present invention, and that the semiconductorsubstrates may be undoped, P-doped, or N-doped. Suitable materials forthe substrates include but are not limited to silicon, gallium arsenide,germanium, gallium nitride, aluminum phosphide, Sil-xGex and AlxGal-xAsalloys, wherein x is greater than or equal to zero and less than orequal to one, the like, and combinations thereof. Additional examples ofmaterials for use, methods, and terms used in accordance with thepresent invention are set forth in the following references:“Semiconductor Device Fundamentals” by Robert F. Pierret, p. 4, Table1.1, Addison-Wesley, 1996; “Soft Lithography and Microfabrication,” byC. Brittain, K. Paul, and G. Whitesides, Physics World 1998, 11, 31-36;“Patterning Self-Assembled Monolayers: Applications in MaterialsScience,” by A. Kumar, H. A. Biebuyck, and G. M. Whitesides, Langmuir,1994, 10, pp. 1498-1511; “Fabrication and Imaging of Two-DimensionalPatterns of Proteins Adsorbed on Self-Assembled Monolayers by ScanningElectron Microscopy”, by G. P. Lopez, H. A. Biebuyck, R. Harter, A.Kumar, and G. M. Whitesides, Journal of the American Chemical Society,1993, 115, pp. 10774-10781; “Micro-Stamp Patterns of Biomolecules forHigh-Resolution Neuronal Networks,” by D. W. Branch, J. M. Corey, J. A.Weyhenmeyer, G. J. Brewer, and B. C. Wheeler, Medical and BiologicalEngineering and Computing, vol. 36, pg. 135-141; “Patterning of aPolysiloxane Precursor to Silicate Glasses by Microcontact Printing,” byC. Marzolin, A. Terfort, J. Tien, and G. Whitesides, Thin Solid Films,1998, 315, 9-12; “Soft Lithography”, by Y. Xia and G. M. Whitesides,Annual Review of Material Science, 1998, 28, pp. 153-84; “PrecisionPatterning of PDMS Thin Films: A New Fabrication Method and ItsApplications,” by K. Ryu, C. Liu, 6th International Symposium on MicroTotal Analysis System (μTAS), Nara, Japan, 2002; and “Contact-InkingStamps for Microcontact Printing of Alkanethiols on Gold,” by L.Libioulle, A. Bietsch, H. Schmid, B. Michel, and E Delamarche, Langmuir,1999, 15, pp. 300-304.

[0068] Although the invention has been described and illustrated withreference to specific illustrative embodiments thereof, it is notintended that the invention be limited to those illustrativeembodiments. Those skilled in the art will recognize that variations andmodifications can be made without departing from the spirit of theinvention.

1-43. (Cancelled).
 44. A method for contact printing comprising:positioning a scanning probe microscopy probe having a tip near asubstrate, wherein ink is transferred from the tip to the substrate, andwherein the tip comprises a polymer; and forming the probe by forming astructural layer on a substrate, wherein the substrate forms a cavity,and a sacrificial layer is located between the substrate and thestructural layer.
 45. The method of claim 44 further comprisingselectively removing the sacrificial layer.
 46. The method of claim 44further comprising releasing the structural layer from the substrate.47. The method of claim 44, wherein the cavity forms a pyramid.
 48. Themethod of claim 44, wherein the structural layer includes a tip layer inthe cavity and a beam layer on the tip layer.
 49. The method of claim48, wherein the tip layer comprises an elastomer.
 50. A method forcontact printing comprising: patterning a first ink on a flat surface ofa scanning probe microscopy probe to form an ink pattern on the flatsurface; and positioning the flat surface near a first substrate,wherein the ink pattern is transferred from the flat surface to thefirst substrate, and wherein the flat surface comprises a polymer.
 51. Amethod for contact printing comprising: patterning a first ink on a flatsurface of a scanning probe microscopy probe to form an ink pattern onthe flat surface; positioning the flat surface near a first substrate,wherein the ink pattern is transferred from the flat surface to thefirst substrate; patterning a second ink on the flat surface; andforming the probe by forming a structural layer on a substrate, thestructural layer having a tip layer and a beam layer, wherein thesubstrate forms a cavity, the tip layer is in the cavity, the beam layeris on the tip layer, and a sacrificial layer is located between thesubstrate and the tip layer; and by patterning the structural layer.